The present invention relates to a shaped body, preferably plate-shaped, for use as heat insulation. The present invention also relates to methods of making shaped heat insulation products.
The production of heat insulation plates or flat, level heat insulation bodies based on precipitated silica which are evacuated and provided with a multi-layer casing is known.
Thus, EP-A 0 190 582 and EP-A 0 254 993 describe a casing of compound films which additionally contain a metal film of for example aluminum. These films should be airtight and watertight.
EP-B 0 164 006 describes heat insulation plates which contain fine metal oxides and are evacuated. The casing material can be a compound film with a layer sequence of thermoplastic material/metal film/thermoplastic material.
Published Japanese Patent Application Sho 62-207 777 describes heat insulators which are produced by dispensing perlite or other readily porous materials into a container of hot-sealable plastic laminate and then evacuating the interior of this container.
Hot-sealed, heat-insulating elements consist of plastic laminate 25/m thick with a water-vapor permeability of 1.0 g/m.sup.2.d at 38.degree. C. and 90% relative humidity as well as an oxygen permeability of 2.0 cm.sup.3 /m.sup.2.d at 23.degree. C. and 90% relative humidity. The laminates consist of vinylidene chloride--vinyl chloride copolymer which is vapor-deposited on at least one side with a layer of aluminum 100 to 1000 angstroms thick. At least one laminate layer is used.
The known usage of metal-coated compound films has the disadvantage that heat can be conducted parallel to the film surface, which results when used in insulation materials in undesired thermal bridges on the edges of a heat insulation body between the cold side and the warm side.
The disadvantageous influence on the total thermal conductivity of a heat insulation body associated therewith is not detected in the measurement of thermal conductivity according to the absolute one-plate method with protective ring technology according to Kohlrausch (F. Kohlrausch: "Praktische Physik", vol. 1, 22d edit., B. G. Teubner Verlag, Stuttgart, 1968, p. 375 ff).
A heat insulation body manufactured in accordance with EP-A 0 190 582 using a film containing metal exhibits a thermal conductivity of 8 mW/(m.K), measured in accordance with the above-named method. If a measuring arrangement without protective ring is selected, the thermal conductivity rises, as a function of the geometry and size of the form body and of the thickness of the metal layer in the casing film, to values which are in part considerably higher. The insulating performance of the total heat insulation body thus also depends decisively on whether the casing film used in the productions contains metal or not.
There is thus the problem of producing heat insulation bodies which exhibit a low thermal conductivity both transversally as well as also longitudinally to the course of the compound film.